It is known to fit a helicopter with a sight—or vision system—that is located above the main lift and advance rotor of the helicopter, as described in particular in U.S. Pat. Nos. 4,275,992, 4,447,023, and 5,461,796.
The third of those patents describes a gun-sight device suspended from the top of a mast supporting the sight; the mast extends inside the hollow shaft for driving the rotor in rotation, and its bottom end is secured to the bottom of the case of the main gearbox (MGB).
Such a sight-support mast is generally hollow and receives electric cables or harnesses and/or fluid-transport ducts for transporting a cooling fluid, for the purpose of powering the vision system and conveying signals between the vision system and the cockpit, and also for cooling the optoelectronic components of the sight.